I believe your comments are technically correct (the best kind of correct!) but I think the initial comment is misleading. Describing websites as "more guesswork-laden" suggests (to me) that the same information is elsewhere but more exacting. AFAIK, products like Zestimate aren't offered by other websites (and, if they are, I suspect they're similarly accurate at best). It's a mildly (or maybe dubiously) accurate prediction that's an added feature not offered elsewhere. I don't really see additional optional features as a negative variable.

If I correctly understand what you're saying, brokers of MLS listings simply provide a service in exchange for money...just like any business that provides a service. Sometimes listings are only offered to certain brokers just like products in other industries. More features cost more money (like my iPhone with increased memory).

If this is actually pulling from recent MLS listings rather than... sites like Zillow or Trulia

It seems (although I could be wrong) Zillow and Trulia receive MLS listings in the same manner as brokers. In this way, their MLS listings are just as recent as other brokers. The only difference is that they have additional listings that can't be updated through, say, APIs. I can see how this could be negative but I also see Zillow has a feature to limit searches by those offered by agents. In this way, the option to see (possibly outdated) listings by owner seems like a neutral option at worst (simply don't use it) or positive benefit. Does Zillow really not
"[pull] from recent MLS listings"?

so sites like Zillow are far from the last-word in finding available real estate in a location

I suspect nothing is the "last word". Real estate is sales and sales is persuasion and negotiation. In any scenario, short of being naive about the internet, I would be perplexed by anyone who is "duped" by a higher price on one website. Presumably do some research (even if it's simply searching for the house on Google) before dropping hundreds of thousands of dollars. Buying a house isn't like buying toilet paper on Amazon; there is no 'buy' button whereby you're locked into higher price because you didn't check for less expensive vendors. The economics are very different when every vendor is selling the same toilet paper.

Finally, circling back to my question, what other websites implement the same pre-browse requirements?